Abstract
The aim of the present study was to determine the ventilation/perfusion ratio that contributes to hypoxemia in pulmonary embolism by analyzing blood gases and volumetric capnography in a model of experimental acute pulmonary embolism. Pulmonary embolization with autologous blood clots was induced in seven pigs weighing 24.00 ± 0.6 kg, anesthetized and mechanically ventilated. Significant changes occurred from baseline to 20 min after embolization, such as reduction in oxygen partial pressures in arterial blood (from 87.71 ± 8.64 to 39.14 ± 6.77 mmHg) and alveolar air (from 92.97 ± 2.14 to 63.91 ± 8.27 mmHg). The effective alveolar ventilation exhibited a significant reduction (from 199.62 ± 42.01 to 84.34 ± 44.13) consistent with the fall in alveolar gas volume that effectively participated in gas exchange. The relation between the alveolar ventilation that effectively participated in gas exchange and cardiac output (V Aeff/Q ratio) also presented a significant reduction after embolization (from 0.96 ± 0.34 to 0.33 ± 0.17 fraction). The carbon dioxide partial pressure increased significantly in arterial blood (from 37.51 ± 1.71 to 60.76 ± 6.62 mmHg), but decreased significantly in exhaled air at the end of the respiratory cycle (from 35.57 ± 1.22 to 23.15 ± 8.24 mmHg). Exhaled air at the end of the respiratory cycle returned to baseline values 40 min after embolism. The arterial to alveolar carbon dioxide gradient increased significantly (from 1.94 ± 1.36 to 37.61 ± 12.79 mmHg), as also did the calculated alveolar (from 56.38 ± 22.47 to 178.09 ± 37.46 mL) and physiological (from 0.37 ± 0.05 to 0.75 ± 0.10 fraction) dead spaces. Based on our data, we conclude that the severe arterial hypoxemia observed in this experimental model may be attributed to the reduction of the V Aeff/Q ratio. We were also able to demonstrate that V Aeff/Q progressively improves after embolization, a fact attributed to the alveolar ventilation redistribution induced by hypocapnic bronchoconstriction.
Highlights
Hypoxemia is one of the most important clinical signs of pulmonary embolism (PE)
The study was conducted in the Núcleo de Medicina e Cirurgia Experimental of the State University of Campinas (UNICAMP) and was approved by the Ethics Committee for Animal Research of the Institute of Biology, UNICAMP
The increase in VDalv subtracts a considerable fraction of alveolar ventilation, leading to reduction of VAeff [15]
Summary
Hypoxemia is one of the most important clinical signs of pulmonary embolism (PE). The complex abnormalities in gas exchange that occur are multiple, but the literature remains unassertive to elucidate the underlying mechanisms [1,2,3,4,5,6,7,8,9,10].Analysis of the mechanisms involved in the genesis of this severe hypoxemia in humans with PE is difficult because of the multiple variables associated, including car-Braz J Med Biol Res 39(9) 2006 diopulmonary disease [8,9]. Analysis of the mechanisms involved in the genesis of this severe hypoxemia in humans with PE is difficult because of the multiple variables associated, including car-. Several mechanisms are believed to be responsible for hypoxemia. These include low-partial oxygen pressure in mixed venous blood (PvO2), the mismatch between ventilation and perfusion, the intrapulmonary shunt, the diffusion limitation, and the severity of the embolism, impairing the identification of the real cause of hypoxemia [8,9]. The mechanisms responsible for gas exchange have been investigated with the use of the multiple inert gas elimination technique [9]
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